Thermotropic liquid-crystalline polyester resin (hereinafter, called as “liquid-crystalline polyester resin” or “LCP”) is exhibits good flowability on molding and excellent thermostability, and therefore, widely used for manufacturing molded articles, especially, electronic components having thin and small parts such as fine pitch connector. LCP also has good mechanical properties including good rigidity as well as excellent chemical resistant, and gas barrier properties and exhibits high dimensional accuracy. Due to those properties, LCPs are used not only for manufacturing molded articles but also for a variety of products including fibers and films.
Recently, secondary fabrication of molded articles, fibers or films made of LCP is attracting attention of the art. Among the conventionally known secondary fabrication methods, joining methods such as bonding and welding have gotten a lot of attention. In particular, a method widely used for fabricating multipurpose plastics, i.e. methods for welding resin parts, which utilizes frictional heat, have been expected as candidate for fabricating liquid-crystalline polyester resin parts.
However, the widely-distributed conventional liquid-crystalline polyester resins have extremely high melting point as high as 280-400° C. and therefore, LCPs might not be welded by the conventional welding method, or even if they could, the joint portion of the obtained welded product might be too weak to be practically used. Some improved methods for welding liquid-crystalline polyester resin parts have been proposed. For example, JP A H03-184830 discloses an improved method for ultrasonic welding of resin with high melting point such as liquid-crystalline polyester resin, which comprises preliminarily heating the resin to a certain range of temperatures and then, welding the resin. This method can assure the joining in the ultrasonic welding technique.
Specifically, in the method, resin parts to be jointed such as LCP with melting point of higher than 250° C. are preheated by means of an external heating equipment such as air-oven or by heating the support which can be heated by means of heating medium or a heating device and thereafter, ultrasonic welding is carried out. Said method can assure the welding and decrease deformation or failure of the molded articles to be welded.
However, the method is not satisfactory in view of cost and efficiency because of the additional pre-heating step which requires an external heating device or internal support heating equipment. Moreover, the method is not practical because of softening or deformation of the welded articles due to high pre-heating temperatures.